εἰργάζοντο λογάδην φέροντες λίθους καὶ ξυνετίθεσαν ὡς ἕκαστόν τι ξυμβαίνοι → they went to work bringing the stones as they picked them out and put them together as each one happened to fit
pf. Act. de βάλλω.
βέβληκα: pf. к βάλλω.